antlr4 maven plugin: need to create grammar documentation

[Ernst Reissner]

I use antlr4 for some long time and in various projects almost always in conjunction with maven,
and so i use the antlr4 maven plugin.

I would like to use a goal antlr4:docs to create documentation of a grammar.
Currently, documentation of  a grammar or of a rule therein
goes into the parser created and then into javadoc.
I feel it is more appropriate to have a separate documentation.